Objective Methods for Preoperative Assessment of Functional Capacity

Metadata

Author: E. Silvapulle
Full Title: Objective Methods for Preoperative Assessment of Functional Capacity
Category: #books

Highlights

_V O2 peak (i) (ii) Anaerobic threshold (iii) Ventilatory efﬁciency at the AT These variables are derived directly from CPET. (Page 2)
Stress echocardiography, using either exercise stress echocardiography (ESE) or dobutamine stress echocardiography (DSE), may identify inducible ischaemia and thus the presence of signiﬁcant coronary artery disease. These tests have very good ability to exclude coronary artery disease and identify individuals at low risk of postoperative cardiac complications (negative predictive value >0.95). (Page 2)
_V O2 max. _V O2 per Oxygen uptake, or the rate of oxygen consumption ( unit weight per unit time), is one of the most important vari_V O2 peak is the peak rate of oxygen uptake when ables in CPET. the individual exercises up to symptom limitation or fatigue. _V O2 peak reﬂects an individual’s ‘best effort’ and is distinct _V O2 max, a physiological endpoint, refers to from maximum cardiac output and oxygen extraction and is identiﬁed by a plateau in oxygen uptake, despite an increase in _V O2 max during workload.9 Most individuals do not reach their _V O2 max in clinical practice. CPET, which limits the utility of (Page 2)
However, DSE is not a direct measure of functional capacity, and both ESE and DSE have modest sensitivity for identifying individuals at increased risk of 30-day postoperative cardiovascular complications (sensitivity of 0.68 and 0.79, respectively) (Page 2)
(cid:3)1 was associated with low risk of postoperative complications _V O2 peak > 20 ml kg (cid:3)1 min (Page 2)
(cid:3)1 min _V O2 peak < 12 ml kg (cid:3)1 was associated with signiﬁcantly increased risk of postoperative pulmonary complications and mortality (Page 3)
During strenuous exercise, muscle oxygen requirements eventually exceed the capacity of the cardiopulmonary system to deliver oxygen, beyond which anaerobic metabolism _V O2) at which takes place. The AT is the oxygen uptake ( anaerobic metabolism occurs (Page 3)
_V O2 for individuals undergoing non-cardiac surgery, (cid:3)1 is considered the threshold associpeak < 15 ml kg ated with increased risk of perioperative complications (cid:3)1 min (Page 3)
(cid:3)1 has (cid:3)1 min AT < 11 ml kg been accepted as the threshold associated with increased perioperative risk in individuals undergoing non-cardiac sur_V O2 peak, there is slight variation of this gery; as with threshold across surgical cohorts.7 (Page 3)
_V O2 peak of 15 ml .6 As noted in Part 1 of this series, a (cid:3)1 corresponds to 4.28 metabolic equivalents, which kg is considered to approximate the metabolic cost of major surgery.1,2 (cid:3)1 min (Page 3)
_V E/ _V CO2 relationship, Ventilatory efﬁciency is described by the the ratio of minute ventilation to carbon dioxide production. This ratio refers to the volume of air that needs to be ventilated _V CO2 to exhale 1 L of carbon dioxide, per unit time. Therefore, is a measure of the efﬁciency of gas exchange during exercise. _V CO2 at AT is often In the assessment of dyspnoea, measured, as this identiﬁes the point when ventilatory drive increases relative to workload _V E/ _V E/ (Page 4)
_V CO2 at AT ratio _V O2 peak is > 34 deﬁnes ventilatory inefﬁciency.4Whereas _V E/ _V CO2 at AT inﬂuenced by subject motivation, both AT and are effort-independent, and therefore are more reproducible measures of exercise capacity. _V E/ (Page 4)
The 6MWT measures how far a patient can walk up and down a ﬂat, 30 m corridor in 6 min. The measurements obtained include the 6-min walk distance (6MWD), oxygen saturation, heart rate, modiﬁed Borg dyspnoea scale and leg fatigue (Page 4)
The median 6MWD for healthy individuals is between 500 and 600 m (Page 4)
Normal values for the ISWD vary with age, but are usually between 560 and 820 m in healthy individuals (Page 4)
During CPET, the patient is required to perform incremental exercise on an upright cycle ergometer, whilst breathing through a mouthpiece. The patient follows a standardised protocol up to limitation by symptoms. The test provides assessment of the integrative exercise responses involving the cardiovascular, pulmonary and musculoskeletal systems. Data obtained during CPET include heart rate, non-invasive _V O2 ), carbon diblood pressure, 12-lead ECG, oxygen uptake ( _V CO2 ), oxygen saturation, gas ﬂow rates and oxide production ( work rate. (Page 6)
The role of CPET includes measurement of exercise capacity in individuals with unknown or suspected poor exercise tolerance, differentiation of the cause for exercise limitation and risk stratiﬁcation to assist with perioperative planning and appropriate allocation of resources (Page 6)
_V E/ _V O2 peak, AT _V CO2 at AT are the most commonly used variables for and perioperative risk stratiﬁcation. However, these are global measures of physical ﬁtness and, therefore, are not useful in differentiating cardiovascular, respiratory, musculoskeletal or metabolic causes of exercise limitation. (Page 6)
A 6MWD > 510 m was identiﬁed as the threshold that is associated with signiﬁcantly increased chance of DFS (Page 7)
for non-cardiopulmonary surgery, CPET may not accurately predict postoperative complications in individuals with poor functional capacity. (Page 7)
Overall, the following thresholds have been established for CPET-derived variables for prediction of in-hospital surgical morbidity, duration of stay in hospital, in-hospital mortality, 30-day mortality and 1-yr mortality (Page 7)
_V O2 peak (cid:4) 16.7e18.2 ml kg (cid:3)1 provides poor-to-fair prediction of complications (AUROC ¼ 0.63e0.77) after major colorectal surgery (cid:3)1 min (Page 7)
CPET is thought to be particularly useful in individuals expected to have a postoperative forced expiratory volume in 1 s (FEV1) < 40% (Page 7)
(cid:3)1 min Anaerobic threshold (cid:4) 10.0e11.1 ml kg (cid:3)1 provides poor-to-good prediction of complications (AUROC ¼ 0.63e0.85) after major abdominal surgery, colorectal resection, major urology surgery and hepatobiliary surgery (Page 7)
(cid:3)1 (or < 35% predicted) has been suggested as a prohibitive threshold for major lung resection.35 _V O2 peak < 10 ml kg (cid:3)1 min (Page 7)
_V E/ _V CO2 at AT > 30.9 provides poor prediction of complications (AUROC ¼ 0.64e0.69) after major colorectal or urologic surgery (Page 7)